Heretofore, it has been known to provide various types of liquid control devices and/or systems for controlling the liquid level in processing tanks, such as used in the plating industry. For example, reference may be had to applicant's aforesaid U.S. Pat. No. 4,234,785. In such applications, it is necessary that the liquid level be maintained in the plating tank since the lowering of the level below the upper end of the .cent.hot zone" of the radiating immersion heaters can result in damage and/or destruction to the heaters and/or tanks making it important to have a low liquid level advance warning and control system.
The applicant's prior U.S. Pat. No. 4,234,785 exemplifies a marked improvement over prior art controls previously in the form of float devices and microswitches which were unreliable and adversely affected by the environment. Other prior art controls have included capacitors and/or proximity switches which are not satisfactory. Though the control system of applicant's prior U.S. Pat. No. 4,234,785 solved many of these problems, it did not provide an advance warning alarm and safety feature. In applicant's prior patent, a low liquid level responsive control device is operated by the exposed "hot zone" of the immersion heater by means of a bi-metallic (normally) thermostat in conjunction with a fail-safe fuse (non-recycling) which acts as a back-up by having a higher temperature rating. Accordingly, it will seem that this type of control system does not provide an advance warning to enable shut-off of specific heaters where the tanks experience a low liquid level. It has been found that this is extremely important particularly in the electronic industries printed circuit and micro-chip manufacturing processes.
This problem can be appreciated when it is recognized that in a typical plating or printing circuit production lines, the lines consist of a series of plating tanks through which the parts to be plated and/or treating are conveyed. In such case, if one tank is shut-down for any reason (i.e., low liquid level) this can cause a shut-down of the entire line resulting in substantial delay in hence, expense.
Accordingly, in the present invention it will be seen an advance warning alarm and safety shut-off system is provided that eliminates the above difficulties and provides an advance warning to the operator. This allows the operator to correct and/or deal with the problem without having to shut-down the entire production line. It has been found that the system of the inventor gives an operator of a high production line at least one hour to correct the problem before having to shut-down the line due to a cold tank.
It has been found that this improved system is relatively inexpensive to manufacture and provides reliable results to maximize the efficiency of continuous plating lines particularly in the printed circuit and micro-chip manufacturing industry. Other advantages and objects to the present invention will become apparent as the following description proceeds when taken in conjunction with the following drawings.